1. Technical Field
The present invention relates to detection of bus connection, and more particularly to an apparatus for detecting bus connection with a detection pin which is not electrically charged during detection, so as to prevent the detection pin from being electrolyzed in water or in a humid circumstance.
2. Related Art
For an electrical connection port supporting Hot-Plug function, a detection mechanism is required in an electronic device to continuously detect whether an electrical connector of a peripheral device is connected to the electrical connection port, so that the electronic device begins to perform a procedure such as handshaking with the peripheral device through the electrical connection port and the electrical connector, thereby establishing a communication connection with the peripheral device.
Please refer to FIG. 1, a typical detection circuit in the prior art is applied in an electrical connection port having a detection pin 1. The detection circuit includes a voltage source 2, a depletion-type field effect transistor 3, and a voltage level detection unit 4. The voltage source 2 is serially connected to a gate of the depletion-type field effect transistor 3 through two resistors 5 and 6, and the detection pin 1 is electrically coupled to the conjunction node of the two resistors 5 and 6.
The voltage level detection unit 4 is also electrically coupled to a drain of the depletion-type field effect transistor 3 through a resistor 7, and a source of the depletion-type field effect transistor 3 is electrically grounded. The voltage source 2 continuously outputs a voltage to the gate, so that the loop between the source and the drain is normally opened, and thus the voltage level detection unit 4 can continuously detect a reference voltage level Vref. When an electrical connector of a peripheral device is connected to the electrical connection port, the detection pin 1 is electrically coupled to a circuit of the peripheral device, bypasses the output of the voltage source 2 to the circuit of the peripheral device, so that a voltage level of the gate of the depletion-type field effect transistor becomes zero, and the loop between the source and the drain turned to be normally closed, and bypasses the reference voltage level Vref to a ground line, so that the voltage level detection unit 4 obtains a voltage level of zero, thereby obtaining a state in which the electrical connector of the peripheral device has been connected to the electrical connection port.
For an electronic device that is usually soaked in water or operated in a humid circumstance, for example, a product conforming to the International Protection Code, seams of the housing thereof is subjected to water proofing. When the electronic device is operated in the water or in the humid circumstance, the waterproof housing hermetically wraps the electronic circuit of the electronic device to prevent moisture from entering the housing. Regarding to the buttons of the electronic device, watertight thin films are adhered to the inner surface or the outer surface of the housing of the electronic device for covering button holes formed on the housing, so as to prevent moisture from entering the housing through the button holes.
In an electronic device conforming to the International Protection Code, an electrical connection port is usually protected with a waterproof cover in an unused state; when the electrical connection port is connected to an electrical connector, the tight connection between the electrical connector and the electrical connection port ensures that moisture does not invade the conjunction area between the electrical connector and the electrical connection port.
However, in a part of waterproof electronic devices, electrical connection ports thereof need to be exposed normally and cannot be regularly protected with a waterproof cover. The detection pin 1 in FIG. 1 is maintained at a non-zero voltage level due to the voltage detection signal continuously output from the voltage source 2. When the electrical connection port is soaked in water or has moisture on the surface, an electrolysis phenomenon occurs to the detection pin 1 in the water since the detection pin 1 is electrically charged to a non-zero voltage level. The electrolysis phenomenon not only corrodes the detection pin 1, but also causes a short-circuit effect between pins in the electrical connection port 120, so that the voltage output from the voltage source 2 is fed back to other pins through the water, and thus a system error occurs in a circuit of the electronic device.
In practice, not every type of electrical connection port is equipped with the detection pin 1, for example, a USB electrical connection port. In the communication protocol of the USB electrical connection port, a peripheral device continuously exchanges messages with an electronic device through a signal transmission pin to detect whether the peripheral device maintains electrical connection with the USB electrical connection port. In the electrical connection port of this type, the signal transmission pin or a power supply pin needs to be continuously in the state in which the voltage level thereof is not equal to zero. Only after the electrical connector of the peripheral device is connected to the electrical connection port, the peripheral device can acquire a drive power and initiate a request message, so that the electronic device obtains a system event that the electrical connector has been connected to the electrical connection port. If the electrical connection port is exposed to water, the above pin will be rapidly corroded due to electrolysis. Therefore, for such electrical connection port, a mechanism capable of enabling or disabling the electrical connection port is required; otherwise, the electrical connection port must be completely prevented from contacting water.